Studies on the confirmation of amino acids. IV. Conformations of serine, threonine, cysteine, and valine

Abstract

Short range intramolecular interaction energies of a few amino acids with γ-atoms are reported and their role in determining the molecular conformation has been again stressed. In serine and threonine, it is unlikely that the Oγ atom will occupy position II in which it is trans to the amino nitrogen. In cysteine, all three staggered positions of Sγ about the bond Cα-Cβ become equally favourable. In valine, there is definite correlation between the orientation of the carboxyl group and that of the two γ-methyl groups. In general, the backbone conformations of these amino acids are very similar to those of aminobutyric acid. The results indicate that even in amino acids containing hetero-atoms in the side group where strong inter molecular interactions are possible, the molecular conformation is determined to a great extent by the intramolecular short range interactions alone.